1. Field of the Invention
This invention relates to disk head assemblies for supporting read/write heads adjacent rotating disks in disk drives and more particularly, to a method and means of attaching a head suspension assembly to a head actuator arm using thermoplastic bonding with a thermoplastic suspension base plate or a thermoplastic actuator arm.
2. Description of the Prior Art
In hard disk drives data are stored on magnetizable surfaces of a plurality of rotatable disks that are mounted in a coaxial stack on a housing of the drive. Transducer heads that write data to and read data from the disk surfaces are supported by an actuator that is mounted on the housing and can be actuated to position the transducer heads in alignment with concentric data tracks defined on the disks. Each transducer head is attached to one end of a head suspension that is connected to an actuator arm that extends from the actuator body. The suspensions include a flexible load beam constructed of light sheet steel that has a bend formed in it. The load beam acts as a spring that forces the head against the disk surface with an accurate pre-load or xe2x80x9cgram loadxe2x80x9d. Air turbulence caused by the rotating disks lifts the heads slightly off of the disks so that the heads fly on an air bearing across the disk surfaces. The air bearing force is counteracted by the suspension gram load. A spring section of the load beam is formed to provide the load force that counteracts the aerodynamic lift force generated by the rotating disk during operation of the disk drive.
A head-carrying suspension is attached to an actuator arm using a base plate that forms a part of the head suspension. The base plate includes a flat flange portion and a cylindrical hub portion or boss. The base plate hub is passed through a load beam clearance hole and the flange is spot welded to the load beam. The combined base plate, load beam and a flexure make up a head suspension, and the suspension typically has the hub of the base plate extending through and beyond the load beam clearance hole or alternatively the hub and load beam clearance hole are aligned and the flange is welded on the opposite side.
The hubs of the suspensions are inserted into an actuator arm boss hole formed through an actuator arm extending from an actuator body, one hub entering an actuator arm boss hole from each end of the hole in a mid arm between the end-most arms. A swage ball is passed through the cylindrical hubs to force the peripheries of the hubs to expand (swage) into tight engagement with the inner peripheries of the actuator arm boss hole. Thus, an actuator arm may carry two suspensions on opposite sides thereof to support two transducer heads in opposing directions, one up and one down.
A typical base plate has two primary regions, a flange region and a hub region. The flange region is a flat portion to which the load beam is welded. This area preferably remains flat and free from distortion so that it serves as a stable mounting feature for the load beam and ideally remains so throughout the swaging operation.
The hub region is an extended boss whose upper end is contiguous with the flange portion and whose lower end passes through boss clearance holes in both the load beam and the actuator arm. The hub region supplies the retention torque between the base plate, which is welded to the load beam, and the actuator arm by plastically expanding and cold working during the swaging operation, creating a press fit with the actuator arm. A problem with this process is that the base plate flange becomes warped by stress from the hub during the swaging operation. Consequently, the load beam, which is welded to the base plate flange, is deformed by the warping of the base plate flange, adversely affecting the gram load on the transducer head. After assembly, the gram load is tested and if not correct the spring section of the load beam is bent appropriately to adjust the gram load to a predetermined standard. This operation may further distort the load beam and adversely affect the dynamic performance thereof
Since the two transducer suspensions are joined to an actuator arm by passing a ball through two hubs in the same hole in the actuator arm, an asymmetry exists in the forces that are exerted on the hubs to make the joints. The transducers face in opposite directions and the hubs on their respective load beams also extend in opposite directions with respect to the direction of passage of the ball through the inner diameters of the hubs. For one transducer suspension, the ball is passed in a direction that tends to place the hub in compressive stress. For the other transducer suspension, the direction of passage of the ball is so as to tend to place the hub in tensile stress. This difference in stresses causes a variance in gram load change and joint integrity between the two swage directions.
It is therefore an object of this invention is to provide a method and means of attaching magnetic recording heads to actuator arms that reduces the large differing stresses and deformations associated with swaging that result in gram load change, joint integrity and gram load change differences between tension and compression swage directions.
A method of bonding a base plate of a head suspension to an actuator arm in which at least one portion of the base plate or the actuator arm is fabricated of thermoplastic. The suspension and actuator arm are clamped together to form a head stack assembly and the thermoplastic is heated with a heating tool that causes the thermoplastic to deform and bond together the base plate and the actuator arm.
This invention encompasses four unique thermoplastic attachment methods:
1) Bonding metal base plates to an actuator arm by passing a thermoplastic cylinder through the inside diameters of the base plate hubs, clamping the suspension/actuator arm assembly together, and heating and expanding the thermoplastic cylinder ultrasonically causing it to deform and bond to the base plate flanges, the hub inside diameter, and the actuator arm boss hole.
2) Expanding and bonding a thermoplastic base plate hub to an actuator arm boss hole by heating the boss portion of the base plate with a slightly oversized ultrasonic horn pin driven through the base plate inside diameter, resulting in a bond between the base plate boss outside diameter and the hole in the actuator arm.
3) Heating and extruding small peaks of thermoplastic base plate flange material, with a pinned ultrasonic horn, through holes in the load beam and into holes in the actuator arm to attach the load beam and base plate to the actuator arm.
4) Heating and folding over a portion of a thermoplastic actuator arm onto the suspension assembly to constrain and bond the suspension to the actuator arm, using an ultrasonic horn with tapered prongs.
The invention has the advantage that it reduces the large stresses and deformations associated with swaging that result in gram load change, joint integrity and gram load differences between up and down facing head.
The invention has the advantage that thermoplastic base plates and thermoplastic actuator arms greatly reduce disk damage in the drive that results from contact between the base plate or actuator arm and disk during a shock event incurred by the drive.